I have just got a price from my local Skoda dealer for supplying and fitting an engine and gearbox protector (sump guard) to my 1999 Octavia TDi. They quote

AFAIK the special tool would be an air driven 'nutsert' inserter - nothing too special tbh.

http://www.prifast.co.uk/nutsert_tools.htm

Got it fitted last week and Marshalled in The Park Stages Rally on Saturday. Sump guard sits a lot lower than the original plastic one so it's a little unnerving to hear the stones rattle and bang off the metal sump guard when going through the forest roads. I'm still taking my time but hopefully the guard can take the knocks and damage isn't being transmitted into the chassis. What experiences are others getting ? should it be much lower?

It has to be lower otherwise any force could easily be transfered into the sump were you to hit anything at speed.

I'm currently working on a guard design of my own that should come in at less than half the cost of the skoda item - and will be a DIY fit.

I'll keep you informed.